« PreviousContinue »
Vegetation. The area is marked by great diversity of vegetation. The highlands of the Malwa plateau margin are generally poorly provided with big trees. The fertile black cotton soil with which the plateau is covered bears magnificent crops, and the country is extensively cultivated. Of the great variety of crops raised the most important are : opium-poppies, wheat, cotton, maize, juar, gram and various oilseeds.
At its western edge, where the plateau drops sharply, the country is extremely rocky and devoid of soil or water, except in the broader valleys, where the Bhils attempt some rude cultivation and their usual food crops are raised.
The eastern tracts of the Mahikantha States Agency and the Southern Rajputana States of Banswara and Dungarpur, forming the northern portion of the area, are generally rough and wild. The vegetation is poor and generally scrubby. The mahua, the mango and the nim are often seen near villages. The chief crops grown are wheat, rice, bajra, gram, cotton, sugarcane and oilseeds.
But for a few reserved tracts in Bariya State the central belt, of the area as a whole is fairly open and poorly wooded. The bigger trees stand singly or in small local groves. Chief amongst
mango, mahua, nim, tamarind, bor, banyan and pipal. Wild date and palmyra palms also occur. The area is characterised by extensive agricultural lands. The chief crops are wheat, juar, bajra, maize, cotton, gram and oilseeds. Chillies and turmeric are also grown.
The greater part of the southern country, consisting of the southern members of the Rewakantha States, is covered with forests, of which the most valuable are in Bariya State. The commonest tree is the mahua, found most abundantly in Bariya and Chhota Udepur. Teak is also abundant, but generally stunted. Tamarind and mango are also very common near the village areas.
A highly intricate and varied gneissic complex represents the oldest formation of the area.
This is continuous with the preAravalli gneissic complex of central Mewar.1
Mem. Geol. Surv. Ind., LXV, pt. 2, pp. 116-140, (1934).
Lying unconformably on this basement gneiss is a metamorphic series consisting of a recrystallised arenaceous and impure calcareous facies along with an extensive development of slaty, phyllitic and micaceous schistose formations. These have a general northerly strike and are continuous with the Aravalli formations mapped farther north in Rajputana.
Quartzites representing the south-western continuation of the Alwar series of the Delhi system of Rajputana have been mapped in the north-western corner of the area.
Acid igneous rocks, intrusive into the Aravalli and the Delhi formations, are widely distributed in the area.
There is a vast hiatus in the chronological sequence subsequent to the development of the Delhi system and the associated igneous rocks in the area. The entire Palæozoic group is absent. The uppermost system of the Mesozoic group is represented by several patchy outcrops of fluviatile and estuarine deposits, the infratrappean formations of the area. These are either calcareous or arenaceous and show no alteration.
Overlying these and often resting directly on the ancient metamorphics are a series of lava flows, mostly basic in composition, the Deccan traps.
No tertiary formations have been seen in the area under review. The Archæans as well as the younger rocks have been irregularly overlaid by post-tertiary deposits of recent and sub-recent soils, kankar, etc.
Table of formations present.
Recent and sub-recent soil.
Recent and Post. Kankar, calcareous conglomerate, laterite, etc.
Bagh beds, Lameta beds, Nimar sandstone.
Near the north-eastern corner of the area, portions of the southern Rajputana States of Partabgarh, Dungarpur and Banswara are occupied by a highly intricate and varied gneissic complex. It is throughout a region of extreme metamorphism and rapid alternation of heterogenous assemblages of rock types, mostly igneous in origin. Very often, on account of intimate intermixture or interfoliar injection, these have entirely lost their distinctive original characters.
Streaky composite gneisses with widely varying texture and composition, associated with granite, aplite, pegmatite and amphibolite, are the chief members of the intrusive complex. Separate mapping of these has not been attempted on account of their intimate association and intermixture. The gneisses have a general northerly foliation strike, and are continuous with the pre-Aravalli banded gneissic complex of Central Mewar 1.
As regards the relative ages of the different members of the gneissic complex, observations in the area under review have been confirmatory to the views expressed on the subject in the memoir on the Geology of Central Mewar '2.
1 Mem. Geol. Surv. Ind., LXV, pt. 2, pp. 116-140, (1934).
Trans. Nat. Inst. Sci. Ind., I, no. 2, pp. 21-23, (1935). ? Mem. Geol. Surv. Ind., LXV, pt. 2, p. 126.
Gneisses and Granites. As a rule, the granites and gneisses are intimately associated with one another and are notable for their acid character. Typical exposures show broad bands and lenticles of coarse or fine-grained granite alternating with banded gneisses, pegmatites and aplites, the whole often injected copiously in every direction with quartz veins and occasional bands of basic intrusive rocks, forming a mass extremely heterogenous in appearance.
In Banswara and Partabgarh granitic texture is much more common than the gneissic. Extensive belts of true gneisses are absent, and massive, homogeneous granites prevail in the Mahi valley of the eastern tracts of Banswara State.
Near Khalda (23° 36' : 74° 34') the granite exposure shows a coarse, sometimes porphyritic rock, consisting of quartz, orthoclase, microcline, green biotite, sphene, ilmenite and apatite (21/661, 6708) and (21/674, 6719)1. Muscovite is occasionally seen (21/582, 6644) and hornblende is also sometimes present (21/643, 6693).
The gneissic forms prevail near Banswara town (23° 33' : 74° 27'). Epidote is a very prominent secondary constituent in the gneiss of this locality. It occurs mainly along joints and as lenticular bands along the foliation. The mineral imparts a striking green and pink banded appearance to the rock (21/575, 6637).
Farther north, in the area between Kotwal (23° 59' : 74° 32') and Morwani (23° 46' : 74° 34') coarse, unfoliated granite is the predominant rock type. Of the constituent minerals felspar is generally weathered or saussuritised, there is often an intergrowth of quartz and felspar, microcline is occasionally present, and biotite, sometimes weathered into chlorite, is the commonest ferro-magnesian mineral. Magnetite and ilmenite are the usual accessory minerals.
In the rocky area between Sarodia (23° 55' : 74° 28') and Khajuri (23° 36' : 74° 36') the intrusive is characterised by the predominance of its felspathic constituent and corresponding subordination or total absence of quartz. The rock may be classed as syenite. The felspar is much weathered. The mafic mineral is invariably biotite with occasionally a little hornblende or chlorite. Among accessory minerals, besides occasional small amounts of quartz, magnetite and ilmenite are often present.
1 Numbers such as 21/661 refer to the registered number of the rock specimen in the collections of the Geological Survey of India, and numbers such as 6708 refer to the registered number of the thin section in those collections.
Pegmatite and Aplite. Veins and dykes of pegmatite and aplite are intimately associated with the gneissic and granitic members of the complex. These show considerable variation of texture and composition. The pegmatite is composed of varying amounts of quartz and felspar. More or less regular intergrowths between the quartz and the felspathic constituents of the pegmatite, resulting in the characteristic graphic texture often readily discernible in handspecimens, have been noticed in several places. An almost continuous belt of graphic granite with an average width of three to four miles, running north and south along the east bank of the Mahi, has been found penetrating through the gneiss north of Bankawara (23° 38' : 74° 8').
Muscovite is occasionally present in the pegmatite as an accessory constituent. The pegmatite generally shows effects of intense shearing and torsion, often resulting in much crumpled foliated bands interfolded in the gneisses in which they are intrusive.
Besides pegmatite and aplite, veins of felspar have also been noticed at numerous places in the area covered by the gneissic complex. Generally these are much fractured and crushed.
A noteworthy instance of an autoclastic agglomerate composed of fairly large fragments of plagioclase felspar cemented by infiltrated silica, has been noted in the gneissic rocks south of the peak 1190 (23° 43' : 74° 25').
The northern margin of the syenitic belt, south of Sarodia (23° 55' : 74° 28') is marked by satellitic dykes and veins of felspar porphyry. The rock exhibits much weathered and saussuritised orthoclase phenocrysts along with specks of accessory biotite and ilmenite in a granular or crypto-crystalline matrix of quartz and felspar.
Occurrences of aplite containing quartz with orthoclase and plagioclase and also micrographic intergrowth of quartz and felspar have often been recorded in the gneissic complex. Epidote, chlorite and sphene are the common accessories of the aplitic intrusives.
Veins of quartz, generally much broken, are common in the gneissic area. These have not only accompanied all the acid intrusives but have also been found to be intrusive in the basic members of the complex.